The present invention generally relates to a transistor having electrode films made of a copper alloy, and a method for producing the transistor.
Due to an increase in size of a current TFT (Thin Film Transistor) panel, Al-based wirings having a low resistance are widely used. With recent pervasiveness of large-size televisions, the TFT panels are also becoming larger and larger, so that demand for Cu-based wirings having a lower resistance has been increasing instead of the Al-based wirings so as to lower the resistance of the wirings and the costs of the panels.
When the Cu-based wirings are used for a TFT panel, adhesion to a glass substrate or an underlying film is bad, so that there is such a problem that diffusion of atoms (deterioration of barrier property) occurs between the Si layer, which becomes a underlayer, and the Cu-based wiring. In general, Mo-based or Ti-based barrier metal layers are used in the case of the Al-based wirings.
However, although Mo is easily wet etched, it has a problem that the cost of the material is high. On the other hand, although the material cost of the Ti is relatively low, it has a problem that the wet etching is difficult. These problems contribute to cost increase.
The inventors of the present invention have developed techniques for forming underlying layers by oxygen-mixed sputtering with use of a Cu alloy target, such as Cu—Mg and Cu—Zr (Patent Document 1), or a pure Cu target (Patent Document 2).
By the above-described techniques, an oxide (Cux—Oy, XX—Oy, Cux—Xy—Oz; X is an alloying addition) is formed at an interface of the glass substrate or an underlying layer, and the oxidation layer becomes an adhesion and barrier layer. Further, the Mo-based and Ti-based barrier metal layers become unnecessary, so that a Cu wiring process is possible to realize a low resistance and a low cost. See, International publication Nos. WO2008/081806 and WO2008/081805.